the repair to get things back to normal, again. >> reporter: pg&e uses a device shown in this animation that has sensors to detect welds, and other imperfections. this pipe and others like it raise questions about how well it was made, and by whom. john pierre is chair of the civil engineering department at usc. >> a few days from germany. and one of the questions we may have dress is was it used in 1956 compatible with the kind of quality of steels we're using now? >> that is not an easy go answer. >> it's a major concern. but i want to withhold any opinion as to whether or not we need to rip open, you know, i don't know how many hundreds of miles of lines and replace them. until the ntsb comes back with a report. >> there is a coding to prevent corrosion. pg&e is also busy meeting with mayors and other officials about the pipes on its top 100 list this, is in san carlos that is 100 feet long, 24 inches in diameter. >> we're interested in more of the specifics. you know? what is the situation, and what are we going do about it? when? >> there is an aging infrastructure, we better do so
